The present invention relates to hybrid powered construction equipment having a power-up function.
As a construction machine having a power-up function, a hydraulic excavating machine has been proposed in Japanese Patent Publication KOKAI Gazette No. 5-214746 associated with the application previously filed by the present applicant. This hydraulic excavating machine is comprised of a variable displacement hydraulic pump powered by an engine; an operating valve for controlling a flow of operating oil; and hydraulic actuators for activating the work implement and others, and is arranged such that the operating oil discharged from the hydraulic pump by the switching operation of the operating valve is fed to the hydraulic actuators thereby to operate the work implement and others. This hydraulic excavating machine includes a two-stage relief valve for fixing two maximum pressures for the hydraulic pump operated on a two-stage basis; a cut-off valve for fixing the maximum discharge pressure of the hydraulic pump before relief operation when the pressure of the two-stage relief valve is set to the lower set value; a capacity control system for the hydraulic pump; an absorbed torque displacement valve for controlling the absorbed torque of the hydraulic pump; and a power-up switch.
This hydraulic excavating machine is operated in the following way. By turning the power-up switch ON, controlled pressure from the control pressure source is supplied to the pressure setting cylinder to set the spring force for the two-stage relief valve, thereby to set the two-stage relief valve to the upper relief set value. By supplying the above controlled pressure to the pressure setting cylinder to set the spring force for the cut-off valve, the cut-off function (i.e., the function for decreasing the discharge rate of the hydraulic pump to reduce relief loss, when the discharge pressure of the hydraulic pump is close to the relief pressure) is stopped. By outputting an absorbed torque increasing signal to the absorbed torque variable valve through the controller for the absorbed torque variable valve and/or by outputting an engine output increasing signal to the governor driving unit through the controller for the governor driving unit, the absorbed torque of the hydraulic pump and/or engine output power are increased. In this hydraulic excavating machine, the operation power in the full speed range of the work implement can be increased through one-touch operation of the power-up switch.
The hydraulic excavating machine, however, presents the problem of increased relief loss during operation of the power-up switch, because it employs the two-stage relief valve as a means for increasing the absorbed torque of the hydraulic pump. Although absorbed horse power increases due to increased engine power, this is only the result of emergence of the potential horse power of the engine, and it is therefore impossible for the hydraulic excavating machine to increase operation power more than the full horse power of the engine. Another disadvantage is high noise generation caused by increasing the revolution speed of the engine to increase engine power.
The present invention has been directed to overcoming the foregoing drawbacks and a primary object of the invention is therefore to provide hybrid powered construction equipment capable of making effective use of the output energy of the engine; increasing operating speed while keeping noise level low, and assuring operation power equal to or more than the performance of the engine.
The foregoing object can be accomplished by hybrid powered construction equipment according to the invention having an engine; a hydraulic pump powered by the engine; hydraulic actuators activated by discharge oil from the hydraulic pump; an electric motor working in conjunction with the engine; a dynamo electric generator powered by the engine; and a battery for storing electric power generated by the dynamo electric generator, the construction equipment further comprising a power-up switch disposed in an operating lever or operation panel and a controller which inputs a signal released from the power-up switch,
wherein the controller constantly controls the revolution speed of the engine in response to a signal from the power-up switch and controls the output torque of the electric motor such that torque for assisting powering of the hydraulic pump is output.
In the invention, if the work load of the hydraulic actuators is low and the absorbed torque (the torque of the engine which the hydraulic pump requires in order to drive the hydraulic actuators) of the hydraulic pump is smaller than the output torque of the engine, the extra output torque of the engine actuates the dynamo electric generator so that electric power is generated and this electric power is stored in the battery. In this way, the extra energy of the engine is recovered. If a signal which has been output in response to turning ON of the power-up switch is input to the controller, electric power supplied from the battery works on the electric motor to output torque for assistance in driving of the hydraulic pump, and this assisting torque is added to the output torque of the engine. With this arrangement, the output of the hydraulic actuators can be increased while keeping noise level low. Thus, the output energy of the engine can be effectively used for energy saving.
Preferably, in the invention, during the ON state of the power-up switch, the controller controls the output torque of the electric motor in such a way that the absorbed torque of the hydraulic pump is compared to the rated output point torque of the engine, and if it is determined that the absorbed torque is lower than the rated output point torque, assisting torque is generated up to the proximity of the rated output point torque. With this arrangement, the maximum flow rate of the hydraulic pump during low load operation can be increased (See FIG. 4(a)), so that operating speed can be increased.
Preferably, in the invention, during the ON state of the power-up switch, the controller controls the output torque of the electric motor in such a way that the absorbed torque of the hydraulic pump is compared to the rated output point torque of the engine, and if it is determined that the absorbed torque is equal to or in the vicinity of the rated output point torque, assisting torque is output in an amount which exceeds the rated output point torque. With this arrangement, the operation power equal to or higher than engine performance can be assured while maintaining the maximum flow rate of the hydraulic pump.